Dyes are often added to refrigeration systems to enable one to detect leaks of refrigerant. At the site of the leak, escaping refrigerant containing a dye is visible, thereby enabling one to see the leaking fluid. U.S. Pat. Nos. 3,770,640 and 4,369,120 are directed to the use of visible anthraquinone dyes as a means of detecting refrigerant leaks. However, such dyes may be indistinguishable from other colored fluids which may be present, such as colored fuels and lubricating oils used in engines and motors.
To improve detectability, dyes which fluoresce under ultraviolet light have been developed for use in refrigerant leak detection systems. These are an improvement over daylight visible dyes, which may be difficult to see or to distinguish from non-refrigerant fluids which may be present. Escaping refrigerants containing fluorescent dyes are particularly visible when viewed under ultraviolet light, thereby facilitating the leak detection process.
U.S. Pat. Nos. 4,758,366 and 5,149,453 are directed to leak detection compositions comprising fluorescent, alkyl substituted perylene dyes. However, the patent teaches that such perylene dyes are formulated with mineral oil, which makes them unsuitable for use with many refrigerants and refrigerant lubricants. Also, perylene dyes have been found to have limited temperature stability in systems which have high temperature cycles, such as automobile air conditioning systems.
Reissue Patent Nos. 35,370 and 35,395 describe the use of fluorescent naphthalimide dyes in refrigerant leak detection systems. However, certain naphthalimide dyes have been found to precipitate out of solution in pure hydrofluorocarbon refrigerants at low temperatures, such as below about 5.degree. C.
Many of the existing dyes have been found to be unstable or unsuitable for use at the extremes of high and low temperatures to which refrigerants and refrigerant oils are exposed. In addition, many of these dyes are not sufficiently soluble in the fluorocarbon fluids commonly used in current refrigeration systems. In view of these considerations, the S.A.E. International engineering society has established standards for ultraviolet leak detection dyes used in mobile air conditioning systems. In particular, SAE Surface Vehicle Standard J2297 (issued September, 1996) is directed to "Stability and Compatibility Criteria of Fluorescent Refrigerant Leak Detection Dyes for Mobile R-134a Air-Conditioning Systems" (hereinafter, the "J2297 Standard"), which document is incorporated herein by reference. R-134a is the designation for 1,1,1,2-tetrafluoroethane (CF.sub.3 -CH.sub.2 F) which is a fluorocarbon refrigerant commonly used in mobile, as well as stationary, systems. The J2297 Standard sets forth procedures for testing various properties, including stability, solubility and fluorescence, of dyes which are to be introduced into mobile air-conditioning systems for the purpose of allowing the application of ultraviolet leak detection.
Coumarin dyes are a broad class of dyes derived from coumarin (1,2-benzopyrone) used for many purposes, including coloring textiles, plastics and paints. U.S. Pat. No. 5,286,803 provides a general discussion of coumarin dyes, although it is directed to the use of polymerizable coumarin dyes for the preparation of coumarin dye-containing polymers.
U.S. Pat. No. 5,681,984 discusses the use of a wide variety of dyes in refrigeration leak detection systems, including naphthalimide, perylene, coumarin, anthracene, phenanthracene and thioxanthene. However, there are no examples using any coumarin dyes, and no teaching of any specific coumarin dyes suitable for use in such applications.
Thus, there is a need for a fluorescent dye for use in detecting leaks from refrigeration systems which is soluble in the hydrofluorocarbon refrigerants and able to withstand the extremes of high and low temperature to which such refrigerants are exposed. In particular, there is a need for such a dye which is able to meet the requirements of the J2297 Standard. The present invention fulfills this need.